PC-A: the local machine, from where i want to see the remote machine [Fedora]
PC-B: the remote machine, where the vnc server will be [Ubuntu]
install a vnc client [from where you want to connect] on PC-A

yum -y install vinagre

ssh to the target machine [from PC-A to PC-B], then: [if PC-B is behind NAT, then port forward the ssh port!]
with root on PC-B
you will need the "universe" repositories [ vi /etc/apt/sources.list ]

If you want to make 100% sure it's secure make sure that the only open port on your remote host is port 22, the SSH port. You definitely don't want to see anything on ports 59xx. If they are open then someone can connect directly to VNC. Always use nmap or some other port scanner to verify your open ports when you make firewall changes: